This invention relates to the preparation of rapid curing resin compositions, to the resin compositions per se, and to the use of these resin compositions as adhesives.
For many years the adhesives used to bond wood together to make plywood, laminated beams, furniture, etc., have employed aldehyde condensation polymers of phenol, urea, resorcinol, and other similar compounds. These resins, however, produce adhesives having relatively slow curing rates.
The relatively slow cure rates of these resins have necessitated long press times with concurrent restriction on production when used in the manufacture of laminated beams, plywood and other construction uses. To overcome the slow cure rates many modifications of the above resins have been proposed. Other resins, such as the epoxies, have been proposed, but their expense and certain of their physical properties have limited their use. The resins of this invention employ aldehyde condensation polymers modified with particular amines. These resins not only have rapid cure rates but develop adequate adhesive bond strengths in a short amount of time at ambient temperature, thereby eliminating the need for long press times and application of heat to develop sufficient bond strength.
Mazzucchelli et al, in U.S. Pat. No. 2,557,922, describe the preparation of modified phenol-formaldehyde condensation products by the inclusion of mono-amino diphenyls, diaminodiphenyls, or amino diphenylmethanes alone or as condensation products with formaldehyde. The compositions, when mixed with suitable fillers, are used primarily as electrical insulators.
Edison, in U.S. Pat. No. 1,283,706, teaches that small amounts of p-phenylenediamine may be added to two-stage phenolic molding compound or varnish resins as a catalyst to accelerate the heat cure of these resins. Other patents of which U.S. Pat. Nos. 2,106,486, 2,511,913, 2,582,849, 2,875,160, 2,290,345, and 2,994,669 are exemplary, disclose the use of aromatic amines, especially m-phenylenediamine, in insoluble resins intended as ion exchange materials. It is also well known to make condensation resins from aniline and an aldehyde or to use aniline as a modifier for other condensation resins, as taught by Harvey in U.S. Pat. No. 2,766,218.
Cox et al. in U.S. Pat. No. 3,186,969 describe intermediate products which are further reacted with compounds containing the oxirane group to form vicinal epoxides. The intermediate products are reaction products of an aromatic primary amine, a phenol and an aldehyde. Reaction conditions, however, are carefully chosen to avoid any condensation between the phenol and aldehyde.
Bornstein in U.S. Pat. No. 3,471,443 teaches the use of aniline or aniline salts as cure accelerators in heat curing phenol-formaldehyde resins and gives the same teaching in regard to phenol-resorcinol-aldehyde resins in U.S. Pat. No. 3,476,706. The latter patent also teaches a so-called honeymoon glue system using the disclosed products.
German Pat. No. 358,195 describes resins made by using phenols having basic groups, such as aminophenols, as alkaline catalysts for the condensation of phenol with formaldehyde. The minor amount of catalyst, up to 3 parts per hundred parts of phenol, is cooked together with the phenol and formaldehyde to produce a product suggested as useful for electrical insulation.
Auer, in U.S. Pat. No. 2,309,088 teaches the manufacture of organic isocolloids through modification of resins with amine compounds. The isocolloids are useful, inter alia, as additives for varnishes to improve their alkali and hot and cold water resistance. Fusible phenolic resins containing a natural resin or resinous esters thereof are modified by Auer by heating with particular amines at elevated temperatures "to insure complete dissolution or dispersion of the modifying agent". It is not clear even to Auer whether any chemical reaction takes place between the phenolic resin and amine. However, if there was a reaction, the substituents such as carboxyl groups on the phenolic resins attributable to the natural resin or resinous esters thereof would result in the formation of amides, and not in the formation of the amine modified products of this invention. Amide modified condensation polymers have significantly lower reactivity for purposes of this invention than do amine modified condensation polymers, and are therefore to be avoided. Further, because Auer's phenolic resin starting materials are apparently permanently fusible, it can be inferred that they are novolaks and therefore contain no reactive alkylol groups, making them inappropriate for the practice of the present invention.